As a steering apparatus for applying a steering angle to steered wheels (except in the case of special vehicles such as a forklift, the steered wheels are normally the front wheels), construction such as illustrated in FIG. 12 is widely known. In this steering apparatus, a steering shaft 3 is supported so as to be able to rotate freely on the inner-diameter side of a cylindrical shaped steering column 2 that is supported by the vehicle body 1. A steering wheel 4 is fastened to the rear-end section of the steering shaft 3 that protrudes further toward the rear than the rear-end opening of the steering column 2. When the steering wheel 4 is rotated, this rotation is transmitted to an input shaft 8 of a steering gear unit 7 by way of the steering shaft 3, a universal joint 5a, an intermediate shaft 6 and a universal joint 5b. As the input shaft 8 rotates, a pair of tie rods 9 that are located on both sides of the steering gear unit 7 are pushed or pulled, which applies a steering angle to a pair of left and right steered wheels according to the amount that the steering wheel 4 is operated.
In the construction illustrated in FIG. 12, in order to make it possible to adjust the forward-backward position of the steering wheel 4, an expandable and contractible steering column 2 and steering shaft 3 are used. Moreover, during a collision accident, following the primary collision that occurs when an automobile hits another automobile or the like, a secondary collision occurs when the body of the driver hits the steering wheel 4. However, the steering column 2 and steering shaft 3 include construction for protecting the driver by absorbing the impact energy and allowing the steering wheel 4 to displace in the forward direction. More specifically, construction is employed in which the steering shaft 3 that supports the steering wheel 4 is supported by the vehicle body 1 so as to be able to displace in the forward direction due to an impact load in the forward direction that occurs during a secondary collision. In the construction illustrated in FIG. 12, the steering shaft 3 includes an outer tube 11 and an inner shaft, and together with the outer tube 11 being able to displace in the forward direction as the overall length of the steering shaft 3 contracts due to an impact load during a secondary collision, the steering column 2 that supports the steering shaft 3 includes an outer column 10 and an inner column, and that outer column 10 is supported by the vehicle body 1 so that the outer column 10 is able to displace in the forward direction as the overall length of the steering column 2 contracts. It is also possible for the front and rear positions of the outer column and inner column of the expandable and contractible steering column, and the outer tube and inner shaft of the steering shaft to be opposite that of the construction illustrated in the figure.
On the other hand, as a countermeasure against theft of an automobile, automobiles are equipped with various kinds of anti-theft apparatuses. As one kind of such an apparatus, a steering lock apparatus, that makes it impossible to operate the steering wheel unless a proper key is used, is widely used. FIG. 13 illustrates construction of an example of a steering lock apparatus as disclosed in JP2008-265646 (A). The steering lock apparatus 12 is such that a lock unit 13 is provided in part of the steering column 2a, and a key lock collar 15, on which an engagement concave section 14 is formed in at least one location in the circumferential direction, is fitted onto and fastened to part of the steering shaft 3a whose phase in the axial direction coincides with that of the lock unit 13. When the steering lock apparatus is in operation (when the key is locked), it is possible to substantially unable to rotate the steering shaft 3a by displacing the tip-end section of the lock pin 16, that is a component of the lock unit 13, toward the inner diameter side of the steering column 2a through a lock through hole 17 that is formed in the middle section in the axial direction of the steering column 2a, and by engaging the tip-end section of the lock pin 16 with the engagement concave section 14.
When this kind of steering lock apparatus 12 is assembled in a steering apparatus, the lock unit 13 is provided on the outer-diameter side of the steering column 2a, and the key-lock collar 15 is provided on the inner-diameter side of the steering column 2a. Therefore, in order to place the key-lock collar 15 on the inner-diameter side of the steering column 2a so as to be able to rotate, and to securely engage or disengage the lock pin 16 and the key-lock collar 15 without making the stroke of the lock pin 16 too large, it is necessary to make the thickness of the steering column 2a where the steering lock apparatus 12 is assembled thin by making the outer diameter of the steering column 2a small in at least the portion where the steering lock apparatus 12 is assembled, and making the inner diameter thereof larger.
FIG. 14 illustrates an outer column 10a that is a component of a steering column as disclosed in JP2007-223383 (A). In one end section in the axial direction of the outer column 10a (the left end section in FIG. 14), the other end section of the cylindrical shaped inner column is fitted in a state such that relative displacement in the axial direction is possible. The outer column 10a is made of a light alloy such as an aluminum alloy, a magnesium alloy or the like, and is formed into a single body by casting. A lock through hole 17a is provided in the middle section in the axial direction of the outer column 10a in order for a steering lock apparatus 12 such as illustrated in FIG. 13 to be assembled. When the thickness of this kind of outer column 10a has been made thin, there is a possibility that the strength of the outer column, which is essential when the steering lock apparatus 12 is operated, will not be sufficiently secured. In other words, when trying to rotate the steering wheel 4 (see FIG. 12) with a large force in a state in which the lock pin 16 that protrudes toward the inner-diameter side of the outer column 10a through the lock through hole 17a is engaged with the engagement concave section 14 of the key-lock collar 15 (see FIG. 13), an excessively large force is applied to the peripheral edge section of the lock through hole 17a, and there is a possibility that this peripheral edge section will deform. In order to overcome this problem, it is feasible to form the outer column 10a using an iron alloy. However, then another problem occurs such as the weight of the overall steering column increases.